The present invention relates generally to circuit modules, and more specifically, to a method and assembly for mounting thick integrated circuit packages within a thin circuit module.
Circuit modules or cards are increasing in use to provide storage and other electronic functions for devices such as digital cameras, personal computing devices and personal digital is assistants (PDAs). New uses for circuit modules include multimedia cards and secure digital cards.
Typically, circuit modules contain multiple integrated circuit devices or xe2x80x9cdiesxe2x80x9d. The dies are interconnected using a circuit board substrate, which adds to the thickness of the module. Pre-packaged dies are available for some functions at a lower cost than ball-grid array (BGA) or other mountable die packages, and in the early phases of production, the pre-packaged dies may be the only source of an integrated circuit. Low cost pre-packaged dies are typically available in thin-small-outline packages (TSOP) or thin-quad-flatpack (TQFP) packages, but these packages are still too thick for applications such as secure digital cards, which have total package thickness on the order of 2 mm or less. While the plastic package portion of the integrated circuits are typically on the order of 1.0 mm thick, the leads exit the package at mid-height and have xe2x80x9cS-leadxe2x80x9d forms that provide thermal and other stress relief and standoff above the mounting surface for air circulation. The designs of the above-described packages are adapted for surface mounting above the substrate and make the package height above the substrate unsuitable for circuit module applications.
In order to accommodate the above-described packages, a thin cover could be used, but would require special manufacturing techniques and could not be manufactured or welded to the substrate or outer housing reliably. Additionally, surface mounting to the thin substrates required in circuit modules causes warping of the substrate.
Very thin versions of the TSOP package (VT-TSOP) are being developed, but are not commonly available and are very expensive. Similarly, very thin land-grid-arrays (VT-LGA) are suitable for use within circuit modules but are expensive and not commonly available.
Therefore, it would be desirable to provide a method and assembly for mounting thick integrated circuit packages within a low-profile circuit module. It would further be desirable to provide a method and assembly for modifying packages having standard xe2x80x9cS-leadxe2x80x9d interconnects for use within a circuit module.
An assembly and method for mounting thick integrated circuit packages within a low-profile circuit module permits use of a pre-packaged integrated circuit that would otherwise be too thick for proper incorporation within the circuit module. A straight lead package, which may be a standard xe2x80x9cS-leadxe2x80x9d package, is mounted within a cavity in the circuit module substrate, so that the effective height of the integrated circuit package is reduced.
The circuit module assembly includes the pre-packaged integrated circuit, a carrier including a cavity within which on the pre-packaged integrated circuit is mounted, multiple external contacts coupled to the pre-packaged integrated circuit on the bottom of the carrier for providing an electrical interface to the integrated circuit, and a cover over the top surface of the carrier.
The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings.